2.B.1 Membrane Practice Quiz

1. Which of the following statements is NOT correct about the phospholipid molecules in the plasma membrane?

The polar heads face outward.

The nonpolar tails face inward.

The polar heads are hydrophobic.

The nonpolar tails are hydrophobic.

Explanation

2. The process by which cells expel, or secrete, large molecules is known as

Facilitated Diffusion

Active Transport

Endocytosis

Exocytosis

D) Exocytosis

Both endocytosis and exocytosis are used for the movement of large molecules. The prefix endo- means "within" while exo- means "out of".

Explanation

D) Exocytosis

Both endocytosis and exocytosis are used for the movement of large molecules. The prefix endo- means "within" while exo- means "out of".

3. Which of the following molecules would NOT be found in animal plasma membranes?

Proteins

Phospholipids

Glycolipids

Cholesterol

Nucleic Acids

Explanation

4. Cholesterol found in the plasma membrane of animal cells serves which of the following purposes?

It allows the cell to remove hydrogen atoms from phospholipids.

It makes the membrane less flexible, allowing greater pressure inside the cell.

It allows the membrane to stay fluid more easily.

It allows for polar molecules to easily cross through the membrane.

Cholesterol is a lipid molecule that is found in the plasma membrane of animal cells. It plays a crucial role in maintaining the fluidity and stability of the membrane. By inserting itself between the phospholipids, cholesterol prevents the fatty acid chains of the phospholipids from packing too closely together, which would make the membrane less fluid. This helps to maintain the proper balance between rigidity and flexibility in the membrane, allowing it to function effectively. Therefore, the presence of cholesterol allows the membrane to stay fluid more easily.

Explanation

Cholesterol is a lipid molecule that is found in the plasma membrane of animal cells. It plays a crucial role in maintaining the fluidity and stability of the membrane. By inserting itself between the phospholipids, cholesterol prevents the fatty acid chains of the phospholipids from packing too closely together, which would make the membrane less fluid. This helps to maintain the proper balance between rigidity and flexibility in the membrane, allowing it to function effectively. Therefore, the presence of cholesterol allows the membrane to stay fluid more easily.

5. What is the function of the carbohydrates in the cell membrane?

Pumps and Channels

Communication

Fluidity

Break down organelles

Carbohydrates in the cell membrane play a crucial role in the function of pumps and channels. They act as recognition sites for cell-cell communication and help in the identification of self and non-self cells. These carbohydrates also contribute to the fluidity of the membrane by preventing the close packing of lipids. However, they do not break down organelles, which is not a function associated with carbohydrates in the cell membrane.

Explanation

Carbohydrates in the cell membrane play a crucial role in the function of pumps and channels. They act as recognition sites for cell-cell communication and help in the identification of self and non-self cells. These carbohydrates also contribute to the fluidity of the membrane by preventing the close packing of lipids. However, they do not break down organelles, which is not a function associated with carbohydrates in the cell membrane.

6. Which of the following functions is most important for the glycoproteins and glycolipids of animal cell membranes?

Facilitated diffusion of molecules

Active transport of molecules

Maintaining membrane fluidity

The ability to distinguish one cell from another

Facilitated diffusion of molecules is the most important function for the glycoproteins and glycolipids of animal cell membranes. This process involves the transport of specific molecules across the cell membrane with the help of transport proteins. Glycoproteins and glycolipids play a crucial role in facilitating this process by acting as recognition sites for the transport proteins. They help in the selective transport of molecules, such as ions and large polar molecules, that cannot freely pass through the lipid bilayer. This ensures that essential molecules can enter the cell while maintaining the necessary balance and preventing the entry of harmful substances.

Explanation

Facilitated diffusion of molecules is the most important function for the glycoproteins and glycolipids of animal cell membranes. This process involves the transport of specific molecules across the cell membrane with the help of transport proteins. Glycoproteins and glycolipids play a crucial role in facilitating this process by acting as recognition sites for the transport proteins. They help in the selective transport of molecules, such as ions and large polar molecules, that cannot freely pass through the lipid bilayer. This ensures that essential molecules can enter the cell while maintaining the necessary balance and preventing the entry of harmful substances.

7. Which of the surface molecules found on the cell membrane are thought to be most important as cells recognize each other?

Integral proteins

Peripheral proteins

Cholesterol

Glycoproteins

Integral proteins are embedded within the cell membrane and play a crucial role in cell recognition. They have specific binding sites that allow cells to recognize and interact with each other. These proteins act as receptors and facilitate cell signaling, communication, and immune responses. They are involved in various cellular processes, including cell adhesion, cell-cell recognition, and cell signaling pathways. Therefore, integral proteins are considered the most important surface molecules in cell recognition.

Explanation

Integral proteins are embedded within the cell membrane and play a crucial role in cell recognition. They have specific binding sites that allow cells to recognize and interact with each other. These proteins act as receptors and facilitate cell signaling, communication, and immune responses. They are involved in various cellular processes, including cell adhesion, cell-cell recognition, and cell signaling pathways. Therefore, integral proteins are considered the most important surface molecules in cell recognition.